Fuel cell systems are increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers, such as vehicles, as a replacement for internal combustion engines, for example. Fuel cells are electrochemical devices which combine a fuel such as hydrogen and an oxidant such as oxygen to produce electricity. The oxygen is typically supplied by an air stream. The hydrogen and oxygen combine to result in the formation of water. Other fuels can be used such as natural gas, methanol, gasoline, and coal-derived synthetic fuels, for example.
The basic process employed by the fuel cell system is efficient, substantially pollution-free, quiet, free from moving parts (other than an air compressor, cooling fans, pumps and actuators), and may be constructed to leave only heat and water as by-products. The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack with the plurality of cells commonly arranged in electrical series. Since single fuel cells can be assembled into stacks of varying sizes, systems can be designed to produce a desired energy output level providing flexibility of design for different applications.
Different fuel cell types can be provided such as phosphoric acid, alkaline, molten carbonate, solid oxide, and proton exchange membrane (PEM), for example. The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is coated on one side with a thin catalyst layer. The electrodes, catalyst, and membrane together form a membrane electrode assembly (MEA).
In a typical PEM-type fuel cell, the MEA is sandwiched between “anode” and “cathode” diffusion mediums (hereinafter “DM's”) or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper. The DM's serve as the primary current collectors for the anode and cathode, as well as provide mechanical support for the MEA. The DM's and MEA's are pressed between a pair of electronically conductive plates which serve as secondary current collectors for collecting the current from the primary current collectors. The plates conduct current between adjacent cells internally of the stack in the case of bipolar plates and conduct current externally of the stack (in the case of monopolar plates at the end of the stack).
The bipolar plates typically include two thin, facing metal sheets. One of the sheets defines a flow path on one outer surface thereof for delivery of the fuel to the anode of the MEA. An outer surface of the other sheet defines a flow path for the oxidant for delivery to the cathode side of the MEA. When the metal sheets are joined, the joined surfaces define a flow path for a cooling fluid. The plates are typically produced from a formable metal that provides suitable strength, electrical conductivity, and corrosion resistance, such as 316L alloy stainless steel, for example.
The bipolar plates may include at least one coating applied to the exterior. Typically, the at least one coating is applied using a dipping process. During the dipping process, the bipolar plates are submerged in at least one tank of fluid. Any amount of fluid that enters the coolant channels significantly affects the contact resistance and the uniformity of the current distribution throughout the active area of the bipolar plate, rendering the bipolar plate substantially unsuitable for stack builds. Therefore, the coolant channels of the bipolar plates are sealed during the dipping process. Generally, the fluid is prevented from entering the coolant channels by manually securing metal seal blocks over the coolant channel headers using a plurality of fasteners.
Such seal blocks require the use of additional equipment and tools to seal the coolant channels from the fluid. The additional equipment is excessively heavy and easily susceptible to improper installation.
It would be desirable to produce a container having integrated coolant seals for militating against entry of a fluid into internal coolant channels of bipolar plates during a dip coating process, wherein the container is economical to produce and the complexity of production and use thereof is minimized.